The dielectric is characterized in that it transmits, stores or records the action and influence of external bias electric field signal in an electric polarization manner in which the gravity centers of positive and negative charges do not coincide. Therefore, dielectric constant is a most fundamental parameter which characterizes a dielectric. Ferroelectrics are a special kind of dielectric materials which has a large dielectric constant, a strong non-linear effect, a large strength of spontaneous polarization, as well as significant dependencies upon temperature and frequency. In recent years, ferroelectric thin film based material has been widely used in ferroelectric random access memory (FeRAM), dynamic random access memory (DRAM), non-refrigerating infrared detector, thin film dielectric capacitor, electric field modulated microwave device, AC electroluminescent device and thin film sensor, etc.
In a ferroelectric thin film, e.g., in a ferroelectric capacitor formed based on a ferroelectric thin film, when the direction of external bias electric field is different from the direction of electrical domains, if the voltage for generating the external bias electric field is larger than the coercive voltage (Vc) of the ferroelectric thin film, the ferroelectric domains will move, i.e., the ferroelectric domains will switch their polarization direction; the moving speed of ferroelectric domain which reflects the switching speed of polarization is in direct proportion to the switching current. Generally, the external bias electric field is realized by applying a voltage pulse.
The prior art of ferroelectric analyzing apparatus can make tests on various characteristic parameters of ferroelectric thin film, e.g., remaining polarization charges, domain switching speed. When it is required to adjust the domain switching speed of ferroelectric domains, the amplitude of voltage pulse (i.e., the amount of voltage biased on the ferroelectric thin film) is generally changed so as to realize such an adjustment. This is because during the domain switching, the required charge equals to an integration of current flowing through a ferroelectric thin film over time, and the variation of voltage amplitude will result in variation of the current and further lead to variation of time for the required integration charge, thus making it possible to adjust the domain switching speed of ferroelectric domains.
Obviously, with the method for adjusting the domain switching speed of ferroelectric domains of the prior ferroelectric analyzing apparatus, it is required to change the shape of voltage pulse continuously during adjusting, which is a complicated process and has a demanding requirement on the voltage pulse generator of ferroelectric analyzing apparatus; meanwhile, since the range of variation of the voltage pulse is easily limited by apparatus and instruments, it is difficult to realize an adjustment of domain switching speed of ferroelectric domains in a sufficiently wide range of orders.